As police say fatigue may be partly to blame for a fatal snow plow accident in Medford yesterday, 5 Investigates has found lax rules and few restrictions around snow plow drivers and time behind the wheel, leading some to stay awake for literally days at a time.

In Medford, police tell 5 Investigates that fatigue is one of several possible factors that resulted in a contracted plow driver backing into and killing Whole Foods worker Cesar Moya, 60, of Chelsea. The plows lights were covered with snow and Moya was in the driver's blind spot, police said. The driver, who was from Fall River, was extremely upset at the accident and was praying over Moya when police arrived.

It's no surprise to Newton snowplow driver Joe Lamacchia that plowing can be dangerous work.

"When you're behind the wheel of a plow, the obstacles, and hours, seem endless," he told 5 Investigates' Karen Anderson. "You can't believe what can happen out here to us. It's like 1,000 decisions you have to make every second. "

Those decisions are made often times with little sleep.

"I did 18 to 24 hours (yesterday), Lamacchia says. "I don't like to push (my drivers) any further than that. It's too dangerous."

But pushed is just what many plow drivers are.

"I've heard guys going 40-50 hours, I think it's kind of crazy. How much money do you need?" Lamacchaia said.

Drivers for the state normally can't go for more than eight hours without a break. But those federal limits are thrown out during emergencies like big snowstorms, according to the Massachusetts Department of Transportation.

A MassDOT spokesperson tells 5 Investigates that it's up to the people in charge of the different highway depots to decide when to take a driver off the road. The state has about 4,200 plows to deploy but has several hundred plow drivers on standby to relieve fatigued drivers, the spokesman said.

And there are no standards for plow drivers from the federal Occupational Safety and Health Administration.

In Boston, the mayor's office says Boston limits all its drivers, contractors or city employees, to 16-hour shifts with two 30-minute breaks.